... efficiency advantage:1.rough,fine and finish grinding stone surface2.for machine: manual,multi-heads,automatic machine3.strong grinding ability,low ... high efficiency. Grits: 50#, 200#, 400# with metallic bonded for rough grindingwhereas the grits of 500#, 1500#, 3000# are resin ... bonded for fine and finish grinding. manual machine automatic mahcine multi-head ...